#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
const int INF = 1e9;
const ll LINF = 1e18;
template<class S,class T> ostream& operator << (ostream& out,const pair<S,T>& o){ out << "(" << o.first << "," << o.second << ")"; return out; }
template<class T> ostream& operator << (ostream& out,const vector<T> V){ for(int i = 0; i < V.size(); i++){ out << V[i]; if(i!=V.size()-1) out << " ";} return out; }
template<class T> ostream& operator << (ostream& out,const vector<vector<T> > Mat){ for(int i = 0; i < Mat.size(); i++) { if(i != 0) out << endl; out << Mat[i];} return out; }
template<class S,class T> ostream& operator << (ostream& out,const map<S,T> mp){ out << "{ "; for(auto it = mp.begin(); it != mp.end(); it++){ out << it->first << ":" << it->second; if(mp.size()-1 != distance(mp.begin(),it)) out << ", "; } out << " }"; return out; }

/*
 <url:https://yukicoder.me/problems/no/302>
 問題文============================================================
 =================================================================
 解説=============================================================
 ================================================================
 */

typedef long double ld;
ld solve(){
    ld res = 0;
    ll N,L,R; cin >> N >> L >> R;
    
    L = min(6*N,max(N,L));
    R = min(6*N,R);
    
    if(N <= 9000){ // Nが小さい場合
        vector<vector<ld>> dp(2,vector<ld>(6*N+1));
        int cur = 0,next = 1;
        dp[cur][0] = 1;
        for(int i = 0; i < N;i++){
            for(int j = i; j <= 6*i; j++){
                for(int x = 1; x <= 6;x++){
                    dp[next][j+x] += dp[cur][j]/6.0;
                }
                dp[cur][j] = 0;
            }
            swap(cur,next);
        }        res = accumulate(dp[cur].begin()+L,dp[cur].begin()+R+1,0.0);
    }else{
        ld mu = 3.5*N;
        ld var = 35.0*N/12.0;
        res = (erf((R+0.5-mu)/sqrt(2*var))-erf((L-0.5-mu)/(sqrt(2*var))))/2.0;
    }
    return res;
}
int main(void) {
    cin.tie(0); ios_base::sync_with_stdio(false);
    cout << fixed << setprecision(12) << solve() << endl;
    return 0;
}